Mercury switch



C. W. TRAUTMAN El' AL Sept. 15, 1942.

MERCURY SWITCH Filed July 26. 1940 2 Sheets-Sheet l Mr Il ATTORNEY.

Sept. 15, 1942.

c. w. TRAUTMAN ETAL 2,296,194

` MERCURY swITcH i Filed July ze. 1940 9 2 sheets-sheet 2 il /1 fr? f365.

Pf A7p Patented Sept. 15, 1942 MERCURY SWITCH VCharles T'rautman andHerbert E. Bucklen, IIII, Elkhart, Ind., assigner-s to Bucklen-Beai'Laboratories, Inc., Elkhart, Ind., a corporation of Indiana message anyze, 1940, serial No. 347,678

(orcos-152) 'i'` Claims.

This invention relates to mercury switches, and more particularly isdirected to the metal envelope 'type of mercury switch incorporatingmeans for assisting in the making of the circuit through the switch bymeans of a primary electrode contact member formed of a material whichis substantially unaffected by the constant arcing usually `found in aswitch 4of the metal to mercury contact type.

In the majority of metal envelope mercury switches with Ywhich I amfamiliar, it has been found desirable to provide "an iron elect-rodewhich, in turn, is constantly engaged by a retained body of mercury sothat upon making or breaking of the circuit, the -arcing will occurbetween the retained body and a moving body of mercury to shield themetal electrode from the arcs occurring during the switching operations.This has been considered desirable since the mercury arcs impinging onthe iron electrode have been found to reduce the life of the switch sothat it will withstand only about one-fourth the number of contacts thata switch of the positive mercury to mercury contact type is capable ofwithstanding. However, there are certain advantages in a direct metal tomercury type of c-ontact insofar as snap action switches are concerned,and also in switches which may be employed as drop-cord switches orlevel devices in which a narrow angle is desired.

The present invention contemplates providing the electrode with anaxially inwardly extending disc portion formed of a material such astungsten, molybdenum, or tantalum, which will take the initial arcingwhen c-ontact is made or broken in the switch, and which is notseriously affected by such arcs due to the characteristics of the metalemployed.

This simplifies the internal construction of the switch to aconsiderable extent, since the ceramic may be of simple formationwithout requiring an undercut or groove for the retained body ofmercury, and the electrode construction can be simplified to aconsiderable extent. The disc of arc resisting material is preferably soarranged with respect to the throat or passageway of the ceramicinterposed between the envelope and the electrode as to provide a meansfor preventing splashing of the mercury during snap action, and providesa control capable of insuring positive, clean breaking of the circuitwith no secondary arcing or the like. The arc resisting electrode discserves as a baffle or damper to prevent surging of the mercury andpossible intermittent or secondary contacts thereof with the electrode,which would be the case if the primary disc were not `located theparticular position provided.

Another feature of the present invention is the provision of a verysimple form of switch structure in which a tungsten or molybdenum shankis projected inwardly `from the elebtrode, and is used as the contactmeans for the movable bo'd-y of mercury. This shank or pin may `besecured to the main electrode stud in any suitable manner, such as by apress t, threading, or fstakin'g the same into position. Y

Other objects and advantages of the 'present invention will be moreapparent from thefollowing detailed description which, taken incenjunction with the accompanying drawingswill disclose to those skilledin the art the Vparticular construction and operation of a preferredform of the present invention. v

In the drawings:

Figure 1 is a vertical sectional 'view through `a narrow angle snapaction type of switch oonstruction embodying the present invention;

Figure 2 is a corresponding sectional view through a switch normallyemployed as a drpcord switch or level indicating type of switch;

Figure 3 is a sectional view through a modified form of switch providedwith an enclosing insulating case; and i Figures 4 to 8, inclusive, aresectional views through still further modified forms of switch structureembodying the `present invention.

Referring now in detail to Figure l, we have provided a switch envelope5 of generally elongated cup-shape form having the open end portion 6which is internally bored to'p'rvide the radial shoulder l adjacent theend. The envelope 5 may be formed of any suitable material, such ascol-d rolled stock or the like.

Seated against the radial shoulder l `and centered in the counterboredportion 6 ofl theonvelope 5 is a ceramic insert 8 which is provided withthe frusto-conical throat portion 9 terminating in a radially extendingshoulder Il) against which is seated the electrode disc I2. The di'sc I2is formed of iron or the like, and is thereby centered in and supportedby the ceramic insert 8. The rear face of the electrode disc, as well asthe rear or outer end of the insertf', is engaged by a resilient sealingmember i3, preferably formed of rubber or the like and having theperipheral flange or skirt I4 overlying a tapered Vshoulder on the outerend of the ceramic to proternal wall of the open end of the switch. Thesealing member I3 extends about the shank portion I5 of the electrode,which shank portion extends through the electrode and is provided With ashoulder holding the electrode in engagement with the radial shoulder I0of the ceramic and provided with the reduced inwardly extending portionI6 which, at its inner end carries a metallic disc Il of a diameter suchthat it provides a slight annular opening between its periphery and theinternal surface of the envelope 5. The extending portion I6 of theelectrode shank I5 is provided with a punched over portion I8, whichserves to lock the electrode disc I2 against axial movement relative tothe shank.

A suitable refractory compression member I9 engages the outer face ofthe sealing means I3 and holds the same under compression, this stressbeing exerted through the compression member I9 by means of thespun-over end 29 of the envelope which holds the retaining washer 22firmly against the rear face of the compression member. This compressionmember preferably has a reduced cylindrical extension 23 forming aninsulating barrier between the spun-over edge of the envelope and theshank of the electrode.

The disc II carried at the inner end of the electrode shank is disposedslightly forwardly of the inner end of the ceramic 8, and is preferablyformed of a material which is resistant to mercury arcs, such astungsten, molybdenum or tantalum. A body of mercury 24 is introducedinto the interior of the envelope after the electrode and sealing meanshas been assembled in position within the envelope through thetubulation 25, which tubulation then serves for evacuating the switchchamber 25 and filling the same with an inert gas under pressure, suchas hydrogen. The tubulation is then pinched closed and welded asindicated at 2'I to seal the interior of the switch.

In the operation of the structure thus far described, it will beapparent that when the switch is tilted in a counterclockwise directionthe body of mercury 24 runs along the inner surface of the envelope 5into contact with the disc I1, and

will then be extruded through the annular gap between the periphery ofthe disc and the envelope and up the throat 9 of the insert intosecondary contact with the electrode I2. However, the circuit is made orbroken when the body of mercury 24 contacts the disc I'I, andconsequently any arcing that may occur will occur between the mercuryand the disc I'I. Inasmuch as the disc is formed of an arc resistingmetal, this will have no detrimental effect upon the disc. However, theposition of the disc and its relation to the interior of the envelopeand the ceramic insures that the mercury when moving toward the discwill be trapped thereby on the rear face of the disc, and consequentlywill not have any splashing or vibrating action which might causeintermittent operation of the switch. As a result, a positive making andbreaking of the circuit is provided with no secondary arcing orsputtering, the primary disc I'I serving as a primary contact member,and also as a baffle or dampening means for insuring positive contactand positive breaking of the circuit without any secondary arcing, suchas would be the case if the disc were removed and the body of mercuryallowed to run up the incline and impinge directly upon the electrodeI2. There would be the possibility of it producing either a narrowforwardly extending tongue insufcient to carry the current, resulting insputtering or frying at the leading edge, which contacts the electrode,and thereby producing secondary contacts, which are extremelyundesirable, as well as pitting the face of the electrode.

It will be apparent that this construction provides a narrow angleswitch which can be rapidly operated to produce snap action opening andclosing of the circuit controlled by the switch,

In the form of the invention shown in Figure 2, the switch envelope isadapted to be mounted in vertical position, and is substantiallyidentical in construction with the exception that the envelope 5 has itstubular body portion foreshortened so that when in vertical position thebody of mercury 24', which is of appreciable volume stands at a levelclosely adjacent the tungsten or similar disc I'I. Here again the discacts as a baiile preventing splashing of the mercury within theenvelope, and also serves as the arc resisting medium between which theinitial contact is made from the envelope to the electrode through thebody of mercury. Such a switch may be used for closing the circuit whenthe switch is tilted a predetermined amount from a true verticalposition, or for a pendulum type switch in which the circuit is made atopposite ends of its swing with the disc I'I serving as a bale forpreventing surging movement of the mercury, which might result insecondary contacts.

Considering now the switch shown in Figure 3, there is provided a switchenvelope 3i) having a counterbored portion 32 in which is pressed aceramic insulating member 33 provided with a central bore. Extendingthrough this bore is a tungsten electrode 34 having the inwardlyprojecting end 35 adapted to be engaged by the body of mercury 36 withinthe envelope 30 when the switch is tilted. The electrode 34 is providedwith a shouldered portion 31 seating against the rear face of theceramic bushing 33, and is held in position by means of the resilientcompression gasket 38 fitting about the shoulder and against the rearface of the ceramic 33, which is radially expanded into sealingengagement by means of the ceramic compression member 39 which, ifdesired, may also be formed of hard rubber or the like and which isprovided with the extending reduced cylindrical portion 45 radiallyinsulating the projecting shank of the electrode 34 from the spun-overend 24 of the envelope which locks the retaining ring 43 and the sealingmeans in compressed position. A suitable conductor 44 is secured to theend of the electrode 34 and a second conductor 45 is electrically andmechanically bonded to the envelope 30. A suitable sealing cement orother sealing compound 45 is applied over the end of the envelope aboutthe conductors 44 and 45, embedding them in position to relieve anystresses upon the connections to the electrode and the envelope. Overthe external surface of the envelope there is applied an insulating case41 which may be formed of wood, ber or molded rubber, or the like, andwhich has a closed end portion 48 provided with the openings 49 throughwhich the conductors 44 and 45 are led out. The opposite end of the case41 is open and the case is sealed against displacement from the envelopeby means of sealing material 50 disposed in the open end thereof,thereby locking the envelope within the case. In this form of theinvention the entire electrode 34 is made of a high arc-resistingmaterial, such as tungsten or molybdenum, and

consequently provides a rlow resistance `contact velope. Similar partsare indicated by similar reference numerals throughout these figures. InFigure 4 a metal lenvelope 5l) is provided having the `enlarged end 52provided with the internal shoulder 53 against which is seated theceramic 54. 'The ceramic 54 is provided with a cupysl'iaped recess 55through which projects the 4tungsten `or molybdenum electrode 565-. Asuitable body of mercury 51 is provided in the envelope 5l) and when theswitch is tilted, iiows into position to make contact between theenvelope 50 and the projecting electrode 55. The electrode has its outerend projecting through a -bore in the ceramic 55, and is provided withan annular groove 58, this end of the electrode extending into therecess 59 of the terminal member 59, which may be formed of steel, pureiron, or the like. The terminal member 59 is held in position in therecessed end of the ceramic 54 by means of a resilient compressiongaslret 62,

which is pressed against the shouldered head 63 of the terminal memberby means of the com- Ipression member 64 formed of rigid insulatingmaterial, such as a ceramic, hard rubber, or the like, `the entireassembly being held in compressed engagement by means of the retainingwasher .651and the spun-over end E6 of the envelope. The electrode 5S isheld in the bore of the head y93 of the terminal member 90 by staking`over a portion of the terminal member at the outer end of the bore, asindicated at 61, into the annular groove 58. This iirmly locks themolybdenum or tungsten electrode in place `and -provides a unitaryassembly.

If desired, the interior of the switch chamber may be evacuated throughthe tubulation 68, which is then pinched and welded closed to provideeither a vacuum in the switch chamber, or the switch chamber may be lledwith an inert gas under pressure through the tubulation, as described indetail in the copending application of Paul S. Bear, Serial No. 293,690,filed September 7, 1939.

In Figure 5 a similar construction is provided except that the electrode10 is provided with a threaded end 12 which is threaded into a recessformed in the head portion 13 of the terminal member 14. This also locksthe electrode in position since after the electrode has been threadedinto position, the end of the terminal member 14 is ring staked aboutthe threads to prevent displacement of the electrode, as indicated at15. The electrode 1li in this form of the invention may be eithermolybdenum or tungsten.

In Figure 6 a still further modified form of construction is provided inwhich the electrode 16, which, in this form must be formed ofmolybdenum, is welded as indicated at 11 into a recessed portion in thehead end 18 in the terminal member 19. The nickel welding material mustbe on the end of the electrode 16, as shown, the recess in the head 18ofthe terminal member having a concave bottom to accommodate this weldingmaterial. This firmly secures the electrode in position and provides avery compact and easily assembled construction,

In Figure i7 a still further modification of the switch structure isprovided in which the electrode `8l) extends into a recess 82 in theterminal member 83, and is held -in place by having a shrink fit in thisrecess to compress vthe head portion 8`4 of the terminal member 83 aboutthe =ahigh arc-resisting electrode within a metal lenouter end of theelectrode 8l). With such a shrink fit, displacement of the electrode is`not possible inwardly, and thus a unitary joining of the electrode andterminal member '83 is provided.

Inthe `forms of the invention shown in Figures r3 to `'7, it isimperative that the radial clearance between the electrode and theinternal wall of the envelope be not greater than .122 inch and not lessIthan .062 inch. The purpose of such a clearance is to insure that thebody of mercury will readily Aflow into the annular space between theelectrode and the envelope, and this clearance must be less than the.meniscus height of the mercury in order to effect positive contact asthe .movable body Vof mercury engages `the electrode. .If too small aradial clearance is provided, the

body of mercury will be blocked from flowing into any substantialcontact with the annular surface of the electrode, and only pointcontact will be effected. It is therefore essential that the radialclearance be maintained within the limits specied.

In the form of the invention shown in Figure 8, the envelope 59 isprovided with a counterbored portion `providing the radial shoulderagainst Which the ceramic 85 is engaged. The ceramic 86 is provided withan enlarged outwardly opening recess 81 within which is disposed a coldrolled steel electrode head 88 which is axially recessed in an oppositedirection to receive the outer end of a tungsten electrode 39 projectingthrough the ceramic 85 and extending into the recessed portion of theelectrode head 88. The tungsten electrode is provided with an annulargroove 90 which is ring staked to the electrode head 881as indicated at92. This ,provides a very compact electrode structure in which theelectrode head 88 terminates substantially in the same radial plane asthe outer end of the cemimic-86. The terminal connection to theelectrode head 88 is provided by a spring steel disc 93 which haspressure contact with the outer radial face of the electrode head 88being held thereagainst by the molded rubber gasket 94 compressedtightly thereagainst by means of the retaining washer 95 and thespun-over end 96 of the envelope. The disc has connected thereto theterminal conductor 91 which is soldered or brazed to the disc asindicated at 98, and is provided with the insulating covering 99protecting the conductor 91 from possible radial flashover to the ring95 and end 96 of the envelope. With this construction a switch suitablefor snap action may be provided and, if desired, the switch may beevacuated and filled with an inert gas by means of tubulation |90,although this is not essential. For snap action, the amount of mercuryshown Would be increased since the operating angle of the switch wouldnot be important under such conditions.

It is therefore believed apparent that we have provided a relativelyeconomical switch 'construction which may be either of the unpurnped orthe evacuated type, and in which the end assembly is simplified, whileyet providing for a high arc-resisting metal contact so that the mercurydirectly contacts the arc-resisting electrode, which may be of tungstenor molybdenum, and no retained body of mercury is required.

We are aware that a number of changes may be made in certain of thedetails of the present construction, and we therefore do not intend tobe limited except as defined by the scope and spirit of the appendedclaims.

We claim:

1. A mercury switch comprising a cup-shaped metal shell having a ceramicinsert in the open end thereof, a frusto-conical recess in said insert,an electrode closing the small end of said recess and having anexternally projecting shank extending axially inwardly through saidrecess beyond the inner end of said insert, an electrode disc of arcresisting metal carried on the inner end of said shank in radiallyspaced relation to said shell, said disc being solid and having itsperiphery spaced from said shell a distance less than the meniscusheight of mercury and a body of mercury in said shell adapted to contactsaid disc to close the circuit through said switch and movable past saiddisc through said recess into contact with said electrode.

2. A mercury switch comprising a cup-shaped metallic envelope having aradial shoulder adjacent the open end thereof, a refractory insertseated in said end against said shoulder and having an axially extendingbore therethrough, an electrode having a radially flanged portion seatedin and closing the outer end of said bore and having an axiallyprojecting shank extending outwardly of said envelope and a second shankextending inwardly thereof beyond said shoulder, means forming aresilient seal about the outer radial faces of said electrode flange andinsert, an electrode baffle disc on the inner end of said shank radiallyspaced from the envelope and formed of an arc-resisting metal, and abody of mercury in said switch adapted to bridge between said disc andenvelope to close a circuit therebetween and thence movable into contactwith said shank and flange, said disc thereby taking any arcingoccurring during make or breaking of contact.

3. The switch of claim 2 wherein said disc has its periphery spacedlaterally from the interior of said envelope a distance less than themeniscus height of the mercury to insure that initial making and iinalbreaking of Contact occurs on said disc.

4. In a mercury switch, a cup-shaped metallic switch envelope having aninternal shoulder adjacent the open end thereof, a ceramic seatedagainst said shoulder and having an outwardly facing axial recess, aterminal member having a head end seated in said recess, an electrodeshank of arc-resisting metal secured in said head end and extendingaxially inwardly through said ceramic, said shank terminating at itsinner end in a radial disc of arc resisting metal radially spaced fromsaid envelope wall, sealing means for sealing said ceramic and terminalmember in the open end of said envelope and a body of mercury in saidenvelope adapted to make and break the circuit with said terminal memberby initial contact with said disc.

5. The switch of claim 4 further characterized in that theradialdistance between said envelope and the periphery of said disc lies inthe range between 0.062 and 0.122.

6. The switch of claim 4 further characterized in that the axial innerlface of said ceramic has a concave recess therein about said prong toincrease the exposed lateral surface of said prong and to form a stopfor said mercury body.

7. In a mercury switch, a cup-shaped metallic switch envelope having aninternal shoulder adjacent the open end thereof, a ceramic seatedagainst said shoulder and having an outwardly facing axial recess, aterminal member having a head end seated in said recess, an electrodeprong secured in said head end and extending axially inwardly throughsaid ceramic sealing means for sealing said ceramic and terminal memberin the open end of said envelope, said terminal member terminating shortof said open end, and a terminal conductor having resilient contactmeans at its end held against the terminal member by said sealing means.

CHARLES W. TRAUTMAN. HERBERT E. BUCKLEN, III.

